1. Technical Field
The present invention is directed to an elevator car safety device. More particularly, the present invention is directed to an elevator car safety device which activates when the elevator car moves away from a landing with its door open.
2. Background Information
A typical traction elevator system includes an elevator car connected to a counterweight by a steel cable which passes over a sheave. The sheave, generally located in a machine room at the top of an elevator shaft, is connected to a hoist machine which controls the vertical motion of the elevator car in the elevator shaft.
The hoist machine principally comprises a drive motor and a brake. The drive motor, connected to the sheave in either geared or gearless fashion, controls the rotation of the sheave and thus the travel of the elevator car. The brake, either drum or disk, is directly connected to the sheave and is used to hold the elevator car stationary.
A traction elevator system also includes a safety governor which senses the speed of the elevator car. The safety governor includes a governor rope passing around a safety governor pulley, located in the machine room, down to a tensioning pulley, located at the bottom of the elevator shaft, and back again to the governor pulley. The governor rope is typically connected to a progressive safety mounted on the elevator car. The safety governor detects an overspeed condition of the elevator car based on the fact that the rotational velocity of the governor pulley is proportional to the speed of the elevator car.
Various safety governors are known in the art. For example, in U.S. Pat. No. 4,556,155 issued to Koppensteiner and herein incorporated by reference, a safety governor having two diametrically opposed flyweights located on the governor pulley is shown. As the elevator car travels up and down the elevator shaft, the flyweights move outwardly due to the centrifugal force imparted thereon by the rotating governor pulley.
In an overspeed condition, defined herein as when the speed of the elevator car exceeds a rated speed by a predetermined value, the flyweights are driven outwards and trip an overspeed switch which cuts off power to the drive motor and sets the brake.
If the elevator car speed continues to increase, the further outward motion of the flyweights causes them to trip a mechanical latching device, releasing a swinging jaw which is normally held clear of the governor rope. When the swinging jaw is released, it clamps the governor rope against a fixed jaw, thereby retarding governor rope motion. The retarding action exerted on the governor rope causes safeties located on the elevator car to engage, thereby progressively decelerating and ultimately arresting the motion of the elevator car.
Various safeties are known in the art. For example, in U.S. Pat. No. 4,538,706 issued to Koppensteiner and herein incorporated by reference, a safety having a roller located between the elevator car guide rail and a leaf spring is shown. The leaf spring and guide rail form a triangular section with the roller located at the base of the triangular section during normal operation.
The force exerted on the governor rope causes a safety gear linkage to lift the roller into the tapered portion of the triangular section. The leaf spring exerts pressure on the guide rail via the roller, and the pressure is progressively increased as the roller moves into the tapered portion of the triangular section. The exerted pressure gradually decelerates and ultimately arrests the motion of the elevator car.
During normal elevator system operation, an elevator car is dispatched to a floor, e.g., in response to a hall call and/or a car call. In order to increase the efficiency of the elevator system, it is desirable to have the elevator car door begin opening prior to the car coming to a complete stop at the floor landing. Safety codes permit the elevator car door to begin opening prior to the elevator car coming to a complete stop, provided the elevator car is within a predefined area, commonly referred to as an outer door zone, and is traveling below a predefined speed. The outer door zone is typically 24 inches (600 mm) centered about the floor landing.
The arriving elevator car decelerates and, once within the outer door zone, begins to open the car door. The elevator car will hover at the landing until it is level therewith. Once the elevator car is properly positioned at the landing, the brake is set and the drive motor is shut down. Should the elevator car drift from the landing, the drive motor is re-energized to re-level the elevator car.
Under normal conditions, an engaged drive and a set brake are each capable of holding the elevator car at the landing and/or stationary. However, should either the drive or the brake malfunction, the elevator car can drift away from the landing.
Elevator safety codes are being enacted which require a drifting elevator car to be stopped should the car drift more than a predefined distance with its door open. Specifically, if an elevator car drifts more than 500 mm (about 20 inches) from a landing with its door open, the car must be brought to a complete stop within another 750 mm (about 30 inches).